In one proposed internal combustion engine system, the fuel supply amount is corrected to be larger against the smaller differential pressure between the pressure in an air intake conduit while opening an exhaust recirculation valve and the pressure in the air intake conduit while closing the exhaust recirculation valve (see, for example, Patent Document 1). In this system, it is determined that the degree of clogging in an exhaust gas recirculation conduit or the exhaust gas recirculation valve becomes more against the smaller differential pressure between the pressure in the air intake conduit while opening the exhaust recirculation valve and the pressure in the air intake conduit while closing the exhaust recirculation valve, and determined that the air-fuel ratio is increased. In this system, the fuel supply amount is corrected to be larger and emissions of nitrogen oxides (NOx) are reduced.    Patent Document 1: Japanese Patent Laid-Open No. 2001-349231